Jet printing inks containing polymerized fatty acid-based polyamides

ABSTRACT

The present invention provides an ink suitable for printing with a drop-on-demand ink-jet printer, said ink comprising a colorant, a polymerized fatty acid-based polyamide and a solvent which, taken separately from the ink composition, comprises at least 20% by weight of one or more components containing a single hydroxyl, carbamide, or amide group, said components each having a total of from 5 to 11 atoms of carbon, nitrogen, and oxygen.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to jet printing inks, and to the use ofpolymerized fatty acid-based polyamide resins therein.

2. Description of the Related Art

There is a growing market for all manner of posters, advertisingdisplays, banners, and the like printed by digital methods. One ofthese, impulse printing, also called drop-on-demand (DOD) inkjetprinting, with low-volatility organic solvent-based ink is presentlyused by digital imaging equipment sold by Oce, Gretag, NUR and others toproduce images with better color, adhesion, and abrasion-resistance thanthose images produced with water-based inks. Inkjet printing isperformed by discharging ink droplets from a print head to a substrate.The droplets are ejected through orifices or nozzles in the faceplate ofthe print head and are directed to the substrate to form an imagethereon. In contrast to many other types of printing, there is nocontact between the printer and the substrate in inkjet techniques.

Most of the inkjet printers known in the art may be characterized aseither continuous or impulse devices, depending upon the mechanism bywhich the ink droplets are directed to the substrate. In continuousinkjet systems, an essentially uninterrupted stream of ink is ejectedfrom a nozzle and breaks up into droplets. The droplets bear an electriccharge so that they can be deflected by an applied electric field whichis modulated according to the particular image to be recorded. Theelectric field directs the droplets toward either the substrate or anink re-circulating reservoir. The inks employed in conjunction withcontinuous inkjet systems typically comprise a colorant such as a dye orpigment, an electrolyte to facilitate droplet deflection, and a liquidvehicle to dissolve or disperse the colorant and the electrolyte. Whilethe vehicle in many continuous-type inks comprises water, U.S. Pat. No.4,142,905, in the name of Cooke, disclosed a water-free ink compositionconsisting essentially of a low molecular weight glycol, an inorganicsalt electrolyte, and a dye which is soluble in the glycol.

With so-called “impulse” or “drop-on-demand” inkjet printers, imageformation is controlled by selectively energizing and de-energizing apiezoelectric transducer rather than by modulating an applied electricfield. Ink is stored in the print head or nozzle until it is necessaryto form an image on the substrate. The printer is then activated toapply pressure to the ink and discharge a selected number of discreteink droplets toward the substrate. These ink droplets need not, andtypically do not bear an electric charge. Accordingly, impulse inkcompositions are free of corrosive substances such as water andelectrolytes which continuous stream inks often contain.

However, DOD inkjet printers present a number of problems that are notencountered in continuous inkjet (CIJ) systems. For example, unlike CIJprinters, impulse printers typically are maintained in a stand-by ortemporarily inoperative mode between printing cycles. Thus, the ink isallowed to stand and possibly solidify in the discharge orifices of theprint head. Impulse printers normally begin a printing cycle with suchmaterial in place. Many of the start-up problems encountered withimpulse printers are attributable to ink which has been allowed to standin the discharge orifices during stand-by periods. Such material is lessof a concern in continuous systems because there typically are fewerinterruptions in the flow of ink. Even where ink is allowed to stand andsolidify, it is more easily purged due to the considerably higherpressures at which CIJ printers operate. Accordingly, DOD inks must bespecially formulated to minimize start-up problems.

Although numerous ink compositions for DOD inkjet printers are known inthe art, many of these inks are not suitable for writing on non-poroussubstrate other than vinyl. Some lack adhesion to polyolefin films, andsome are hygroscopic leading to poor wetting and drying. To improve theadhesion of an ink requires use of an improved binder for the colorantin the ink or use of more (by weight) of more of a conventional binder.Yet to improve the economics of DOD printing, jobs must be printedfaster which in turn requires inks that dry faster than many of the inksdescribed in the prior art. Employment of a rapidly evaporating inksolvent is not necessarily the answer. Rapid evaporation of the vehicleof a volatile ink often leads to clogging of discharge orifices becausethe last portion of the ink ejected from an orifice collapses back ontothe faceplate while the rest of the ink droplet breaks away and flies tothe substrate. If the ink that falls on the faceplate dries before itcan flow back into the orifice, a pile of binder resin and colorant willform at the edges of the orifice, gradually changing the way drops aredischarged and even causing the orifice to clog entirely. Rapidevaporation of the vehicle can also clog the orifice during stand-byperiods since the ink forms a meniscus at the air-ink interface and can,as solvent is released to the air, harden. These problems are aggravatedwhen the ink formulator attempts to increase the binder content toimprove adhesion of the ink on the substrate. Moreover, rapidevaporation is undesired due to the adverse environmental and healtheffects of many commonly employed ink vehicles. Finally, if the flashpoint of the ink is too low, generally below about 61° C., it cannot beshipped by air.

Printing inks for flexographic printing on non-porous substrates such aspolyethylene and polypropylene are well known. Those formulated with apigment, a fast-evaporating organic solvent and a resinous binderrepresent the state-of-the-art in packaging printing, allowing printingof high quality full-color images having excellent adhesion andabrasion-resistance even when the package is stored in a freezer forextended periods of time.

The organic solvent in these inks is typically a blend rich in a loweralcohol, for example, ethanol, propanol, or isopropanol, since thesealcohols are good solvents for the resinous binder and evaporate rapidlyafter printing. Flexographic inks may also contain lesser amounts of alower aliphatic ester, such as ethyl acetate and propyl acetate, and anaromatic solvent such as toluene. A common resin is the reaction productof a polymerized fatty acid (also referred to as dimer acid), a diamineor mixture of diamines, and a terminating monocarboxylic acid. Thesepolymerized fatty acid-based polyamide resins suitable for use inflexographic inks are well known and described in detail in numerouspatents as are methods for preparing the inks (e.g., U.S. Pat. Nos.3,253,940, 3,622,604, 3,700,618, and 4,508,868). These patents makeclear that polymerized fatty acid-based polyamides tend to form gelswhen dissolved in lower aliphatic alcohols. Indeed, a large proportionof the issued patents state that they are directed to resin compositionswith improved solution storage stability. Because of these largelysuccessful developments, the stability of commercial flexographic inksis not currently a problem. Nevertheless, no general theory to explainsolution stability has been developed; that is, resins are developedempirically and test results for ethanol and propanol cannot be extendedto other solvents.

These same patents do not discuss the need for a new kind of inksuitable for use in drop-on-demand (DOD) inkjet printers. DOD jet inksmust employ a solvent with a much slower evaporation rate than the loweralcohols so that the nozzle of the printer does not clog. The inks mustalso have a much higher flash point than the lower alcohols so they canbe transported by air and used in an office or small print shopenvironment safely.

There is also an extensive prior art disclosing the preparation of jetinks. A large proportion of said art teaches inks suitable for use inso-called thermal inkjet printers. These inks are largely water-basedand contain no resin. Of the non-aqueous inkjet patents, a largeproportion relate to so-called “continuous inkjet” or CIJ inks. Theseinks are based on low flash point, high volatility solvents such asmethanol, acetone, ethanol, propanol, ethyl acetate, and methyl ethylketone. These inks have been tried in DOD printers but are detrimentalto them since they dry rapidly and tend to clog the heads.

U.S. Pat. No. 4,207,577 (1980) discloses a CIJ ink composition thatnecessarily includes a cellulosic resin, an optional co-resin, acolorant, and at least one solvent. The necessary cellulosic componentcan be cellulose derivatives such as cellulose esters (nitrocellulose,cellulose acetate and the like), and especially cellulose ethers, forexample, methylcellulose, hydroxyethylcellulose, hydroxypropylcellulose,propionitrile cellulose, ethyl cellulose, and benzylcellulose. Thispatent is one of the earliest patents describing a solvent inkjet ink.

U.S. Pat. No. 5,104,448 (1992) discloses low volatility and lowviscosity jet printing inks consisting essentially of a dye (or pigment)and an optional binder, dissolved (or dispersed) in a polyhydric alcoholether solvent (such as polypropylene glycol monoalkyl ether, ethyleneglycol butyl ether, diethylene glycol butyl ether, etc.). This patentmentions that the disclosed ink composition is suitable for DODprinting.

U.S. Pat. No. 5,154,761 (1992) discloses DOD-type inkjet inks whichproduce well-defined images on porous substrates such as Kraft paper andcorrugated cardboard. These ink compositions comprise from 65-80% of alow molecular weight diol, from about 15-25% of a low molecular weightdiol-ether, and from about 1-15% of a colorant. Said inks contain noresin and are not suitable for printing on non-porous substrates.

U.S. Pat. No. 5,594,044 (1997) discloses a jet ink composition suitablefor printing images which have good adhesion and isopropyl alcohol rubresistance, comprising an organic solvent, a urethane resin, a colorant,a cellulose nitrate resin, and an adhesion promoter such as a titanate.Organic solvents suitable for the ink composition of the inventioninclude ketones, esters, C₁₋₆ alcohols, hydrocarbons, glycols, andglycol ethers.

U.S. Pat. No. 5,663,217 (1997) discloses formulation of a jet ink whichcomprises a suspension in a non-aqueous solvent of a disperse phasecontaining an insoluble colorant, a resinous dispersant for thecolorant, and a polymer binder wherein said solvent is a polyhydricalcohol ether. A new component disclosed in this patent is the resinousdispersant, selected to be capable of forming a solution in the chosensolvent and to disperse the dyestuff in the solvent so as to form asubstantially stable dispersion.

U.S. Pat. No. 5,843,219 (1998) discloses inks based on petroleumdistillates. Said inks are stable dispersions comprising pigment,diluent, and a dispersant for stabilizing the pigment in the medium,wherein the major component of the diluent is a hydrocarbon while theminor component is a polar component selected from alcohols, glycols,polyglycols, ethers of glycols and polyglycols, alkoxylated alkylphenols and admixtures thereof.

U.S. Pat. No. 5,888,287 (1999) discloses an inkjet composition having areduced tendency to smear upon application to a substrate. The inkcomposition contains no resin and is free of monohydric alcohol solvent.

U.S. Pat. No. 5,936,027 (1999) discloses a jet ink containing acolorant; a non-aqueous solvent comprising alcohol and ketone, eitheralone or in admixture; and resin comprising ethyl cellulose, phenolicresin, and silicone resin. While perhaps suitable for the CIJ printingmethod, these inks are likely too volatile for use in DOD devices.

U.S. Pat. No. 5,990,197 (1999) discloses an organic solvent-basedpolyester ink formulation containing a fluorescing compound, suitablefor inkjet printing applications. The ink formulation comprises at leastone organic soluble polyester having at least one near-infraredfluorophore copolymerized therein; an organic solvent selected from C₃₋₆ketones, C₃₋₆ organic esters, C₁₋₃ alcohols, and combinations thereof;and 1-5 wt % of a binder selected from cellulose ester, condensedphenolic resin, polyketone, polyamide and polyurethane resin and anorganic solvent soluble electrolyte.

U.S. Pat. No. 5,958,122 (1999) discloses a printing apparatus in whichmetered amounts of an ink and a diluting solution (comprising water andat least one water-soluble or water-insoluble organic component) aremixed and the resulting mixed liquid is ejected to a recording mediumfor jet printing. The water-soluble organic solvent is desirablyselected from aliphatic monohydric alcohol, polyhydric alcohol or itsderivatives, including lower alcohols, alcohol amines, ketones, amides,ethers, alkylene glycols, polyalkylene glycols, lower alkyl ethers ofpolyhydric alcohols, and glycerin.

U.S. Pat. No. 5,998,502 (1999) discloses resinous binders suitable foruse in CIJ printers which are polyamides soluble in ethanol and having aglass transition temperature of at least 95° C. Because ethanol-basedinks are too volatile for use in DOD devices, it is entirely uncertainwhether such binders would be soluble in a solvent appropriate for usein a DOD printer.

U.S. Pat. No. 6,010,564 (2000) discloses a jet ink composition suitablefor printing images on substrates such as plastics, said compositioncomprising an organic solvent, a colorant, a cellulose nitrate resin,and a rosin resin. The organic solvent may comprise one or more organiccomponents, selected from ketones, esters, and C₁₋₆ alcohols. Whilesuitable for the CIJ printing method, these inks are likely too volatilefor use in DOD devices.

The present invention is directed to overcoming these problemsassociated with jet inks, providing jet inks particularly suitable foruse in DOD printers, and related compositions and methods as describedin further detail below.

BRIEF SUMMARY OF THE INVENTION

Interest is being shown by equipment manufacturers in devices to printon polyolefin packaging and plastic-coated boards or plastic sheets. Allof these emerging applications require an ink having good adhesion tothese non-porous substrates in addition to fast drying, excellent colordevelopment and low, stable viscosity. In one aspect, the presentinvention provides inks suitable for this application, and methods ofprinting with these inks.

In another aspect, the present invention relates to organicsolvent-based ink formulations suitable for inkjet printing by thepiezoelectric impulse drop-on-demand (DOD) method, said formulationscomprising a polymerized fatty acid polyamide resin and a suitablesolvent. DOD printers place severe restrictions on their inks, wherethese inks must have relatively low viscosity (about 10-20 centipoise(cps) at the printer's operating temperature) and moderate volatility(evaporation rate of about 2% that of n-butyl acetate). Currentlyavailable DOD inks are based on polymeric resins such as poly(vinylacetate), and solvents such as dipropylene glycol methyl ether. The highmolecular weight of these polymeric resins limits the amount that can beadded to an ink. Thus, another aspect of the present invention is toprovide a resin with a very low molecular weight in order that a muchhigher resin loading can be attained in the ink. This provides fasterdrying inks with improved color development, color permanence, andabrasion resistance.

Polymerized fatty acid-based polyamide resins are known from their usein flexographic printing inks to provide excellent performanceproperties even on polyolefin substrates. However, these resins, thoughcommercially available in a number of grades from Arizona Chemical andother graphic arts industry suppliers, have not been used in makingdigital DOD inks, due in large part because these resins are not solublein the glycol ethers typically used as solvents in commercial DOD jetinks. Nor are they soluble in co-solvents used in DOD inks such ascyclohexanone, ethyl lactate, and ethyl ethoxypropionate, although somedissolve in cyclohexanone but form a gel upon cooling.

Therefore, another aspect of this invention is to provide a preparationfor inks comprising polymerized fatty acid-based polyamide and a solventwhich possess physical properties (such as flash point and evaporationrate) suitable for use in drop-on-demand printing applications.Surprisingly, 1-hexanol, N-methylpyrrolidinone, and similar aliphaticalcohols and amides have been discovered to be excellent solvents inthis regard.

Another aspect of the present invention provides a method of printing,comprising (a) charging a printhead of an ink-jet printer with ink, theink being a fluid mixture comprising polymerized fatty acid-basedpolyamide resin, organic solvent and colorant, wherein the solventcomprises a first solvent and a second solvent, where the first solventis one or a mixture selected from solvents comprising a single amide,single carbamide, or single hydroxyl group as the only non-hydrocarbonmoiety in the solvent; and the second solvent is a hydrocarbon orhydrocarbon mixture; and (b) transferring the ink from the printheadonto a substrate. In a preferred embodiment, the printer is adrop-on-demand printer.

Another aspect of the present invention provides a printing inkcomposition comprising colorant, resin and solvent, where the resin is apolymerized fatty acid-based polyamide resin, the solvent comprises afirst solvent and a second solvent wherein the first solvent is one or amixture selected from solvents having a single amide or carbamide groupas the only non-hydrocarbon moiety in the solvent; and the secondsolvent is a hydrocarbon or hydrocarbon mixture. In a further aspect,the first solvent has a total of 5 to 11 atoms selected form carbon,nitrogen, and oxygen; in a separate further aspect, the second solventis a terpene hydrocarbon. In other optional aspects, the organic solventfurther comprises a third solvent selected from α-hydroxy-carboxylicester, polyalkylene glycol alkyl ether, and ketone-containing solvents;the resin comprises 5-40 wt % of the total weight of resin and solvent;and/or the ink composition has a viscosity of less than 25 cps at one ormore temperatures between 25° C. and 60° C.

Yet another aspect of the present invention provides a printing inkcomposition comprising colorant, resin and solvent, where the resin is apolymerized fatty acid-based polyamide resin, the solvent comprises afirst solvent and a second solvent, where the first solvent is one or amixture selected from solvents having a single hydroxyl group as theonly non-hydrocarbon moiety in the solvent; and the second solvent is ahydrocarbon or hydrocarbon mixture. In a further aspect, the firstsolvent has a total of 5 to 11 atoms selected form carbon and oxygen; ina separate further aspect, the second solvent is selected from mineralspirits and fractions thereof. In other optional aspects, the organicsolvent further comprises a third solvent selected fromα-hydroxy-carboxylic ester, polyalkylene glycol alkyl ether, andketone-containing solvents; the resin comprises 5-40 wt % of the totalweight of resin and solvent; and/or said ink composition has a viscosityof less than 25 cps at one or more temperatures between 25° C. and 60°C.

These and other aspects of the present invention are discussed infurther detail below.

DETAILED DESCRIPTION OF THE INVENTION

One aspect of the present invention provides a method of printing,comprising (a) charging a printhead of an ink-jet printer with ink, theink being a fluid mixture comprising polymerized fatty acid-basedpolyamide resin, organic solvent and colorant, wherein the solventcomprises a first solvent and a second solvent, where the first solventis one or a mixture selected from solvents comprising a single amide,single carbamide, or single hydroxyl group, and the second solvent is ahydrocarbon or hydrocarbon mixture; and (b) transferring the ink fromthe printhead onto a substrate. Preferably, the printer of the presentinvention is a drop-on-demand (DOD) printer.

As used herein, an amide group is a monovalent radical of the structure—C(O)—N(R¹)(R²), or a divalent radical of the structure —C(O)—N(R¹)—,wherein R¹ and R² are independently selected from hydrogen andoptionally-substituted hydrocarbyl radical. A carbamide group is amonovalent radical of the structure —N(R¹)—C(O)—N(R²)(R³), or a divalentradical of the structure —N(R¹)—C(O)—N(R²)—, wherein R¹, R² and R³ areindependently selected from hydrogen and optionally-substitutedhydrocarbyl radical. An hydroxyl group is a monovalent radical of thestructure —OH. “Hydrocarbyl” refers to a hydrocarbon moiety of amolecule, i.e., a moiety composed entirely of carbon and hydrogen atoms.

As used herein, a fatty acid-based polyamide resin is a polyamide resinhaving the structure that results when reactants including diacid anddiamine are reacted together to form molecules containing a plurality ofamide groups, where the diacid includes polymerized fatty acid, andpreferably includes dimer acid resulting from the polymerization of talloil fatty acid.

While is it known to those experienced in the art that polymerized fattyacid-based polyamides are used as resins (or binders) in flexographicprinting inks containing lower alcohols (i.e., C₁₋₅ alcohols, referringto alcohols containing 1 to 5 carbon atoms in their molecularstructures) as diluents, polyamide resins have thus far been largelyavoided in making digital DOD inks. This may be because these polyamideresins do not form fluid, clear, stable, and Newtonian solutions in theglycol ethers, ketones, hydrocarbons, and esters preferred for use inDOD printing inks. Although lower alcohols such as ethanol andisopropanol are widely used to formulate CIJ inks, these solvents drytoo quickly (and thus clog the ink channels) to be useful in DODprinting devices. It is therefore surprising that stable,high-performance DOD inks can be formulated using polymerized fatty acidpolyamides.

The polymerized fatty acid-based polyamides used in the ink compositionof the present invention are preferably and typically clear, amorphous(resinous) solids having a softening point of at least 70° C. and aweight-average molecular weight of 2,000 to 10,000. They are well-knownand result from the reaction of a diacid and a diamine, where at leastsome of the diacid is difunctional polymerized fatty acid, also known asdimer acid. Suitable dimer acids that are commercially available includeUNIDYME™ 18 dimer acid (Arizona Chemical, Jacksonville, Fla.),EMPOL®1019 dimer acid (Cognis Corporation), or PRIPOL™1013 dimer acid(Uniqema Chemical Inc., New Castle, Del.). Suitable diamines include,without limitation, ethylene diamine, diethylene triamine, piperazine,1,2-diaminocyclohexane, trimethylhexamethylene diamine, isophoronediamine, 2-methylpentamethylene diamine (DYTEK™ A, DuPont, Wilmington,Del.) and/or hexamethylene diamine. Optionally, the reactant compositionused to form the polyamide may contain a terminating monocarboxylic acidsuch as (without limitation) acetic acid, propionic acid, isobutyricacid, 2-ethylhexanoic acid, fatty acid monomer, or tall oil fatty acids.Fatty acid monomers may be saturated, monounsaturated, orpolyunsaturated in the hydrocarbon portion of the structure.

As used herein, a saturated fatty acid is one wherein no neighboringcarbon atoms are double-bonded to each other, while a monounsaturatedfatty acid is one wherein one set of neighboring carbon atoms isdouble-bonded together, and a polyunsaturated fatty acid is one whereinmore than one set of neighboring carbon atoms are double-bonded, andwherein no carbon atom is double-bonded to more than one other atom.Exemplary saturated fatty acids are (without limitation) valeric,caproic, caprylic, lauric, myristic, palmitic, stearic, arachidic,behenic, lignoceric, cerotic, and montanic acids; exemplarymonounsaturated fatty acids are (without limitation) caproleic,palmitoleic, oleic, vaccenic, eladic, brassidic, erucic, and nervonicacids; and exemplary polyunsaturated fatty acids are (withoutlimitation) linoleic, linolenic, eleostearic, and arachidonic acids.

Preparative details for polyamides of this invention are disclosed byFloyd and Glaser in U.S. Pat. No. 3,253,940, Sharkey and Sturwold inU.S. Pat. No. 3,700,618, Smith in U.S. Pat. No. 5,407,985, and Ross etal. in U.S. Pat. No. 5,500,209, among many others. In one aspect of theink composition of the present invention, the polyamide is the reactionproduct of reactants comprising polymerized fatty acid, ethylenediamine, hexamethylene diamine, and fatty acid monomer. Illustrative ofpolyamides of this invention are the UNI-REZ® 2000-series polyamide inkresins (Arizona Chemical, Jacksonville, Fla.). Preferred polyamides arethose having a softening point of at least 90° C. and greater than 20%termination by the monocarboxylic acid on an equivalents basis,expressed as $\begin{matrix}{{\%\quad\text{termination}} = {100\% \times \frac{\text{monocarboxylic~~acid~~equivalents}}{\text{total~~carboxylic~~acid~~equivalents}}}} & (1)\end{matrix}$Most preferred are, UNI-REZ® 2221, UNI-REZ® 2224, UNI-REZ® 2215,UNI-REZ® 2226, UNI-REZ® 2228, and UNI-REZ® 2229 polyamides. Preferablythe resin comprises 5-40 wt % of the total weight of resin and solventin the printing ink of the present invention; more preferably the resincomprises 10-35 wt % of the total weight of resin and solvent in theink; still more preferably the resin comprises 15-30 wt % of the totalweight of resin and solvent in the ink.

The liquid vehicle of the ink of the present invention consists of asolution of the selected polyamide dissolved or dispersed in a solventwhich, considered separately from the polyamide and the colorant,consists of two liquid components, designated the first solvent and thesecond solvent. These solvents are preferably organic compounds (i.e.,compounds containing at least one carbon atom in their molecularstructures). The solvents are preferably non-aqueous, i.e., there is nowater in the ink composition of the present invention.

The first solvent, comprising at least 20% by weight of the totalsolvent of the composition (considered separately from the polyamide andthe colorant) is preferably selected from solvents comprising a singleamide, single carbamide, or single hydroxyl group as the onlynon-hydrocarbon moiety in the solvent Exemplary first solvents include(without limitation) liquid aliphatic alcohols, liquid aliphatic amides,aliphatic carbamides, and mixtures thereof. These solvent componentseach preferably have a total of from 5 to 11 atoms of carbon, nitrogen,and oxygen. The first solvent components may be linear, cyclic, orbranched in molecular structure.

Preferably, the first solvent components are selected from the groupconsisting of aliphatic alcohol, aliphatic amide, and polyalkylcarbamide. Illustrative of these are (without limitation) cyclohexanol,1-hexanol, 2-hexanol, 3-hexanol, cis-2-hexen-1-ol, trans-2-hexen-1-ol,cycloheptanol, 1-heptanol, 2-heptanol, 2-ethyl-1-hexanol, 1-octanol,1-nonanol, 3,5,5-trimethyl-1-hexanol, 1-decanol, α-terpineol, and3,7-dimethyl-3-octanol (tetrahydrolinalool) as exemplary aliphaticalcohols; N,N-dimethylformamide (DMF), N-methylpyrrolidinone, andN,N-dimethylacetamide as exemplary aliphatic amides; and dimethylurea,trimethylurea, and tetramethylurea as exemplary polyalkyl carbamides.Preferred are N,N-dimethylformamide (DMF), N-methylpyrrolidinone,N,N-dimethylacetamide, and linear or branched six- to ten-carbon (i.e.,C₆₋₁₀) aliphatic alcohols having a flash point greater than about 45° C.and a viscosity at 25° C. of less than 25 cps. Preferably the firstsolvent is selected from 1-hexanol, 1-heptanol,3,5,5-trimethyl-1-hexanol, 2-ethyl-1-hexanol, 1-octanol,N,N-dimethylformamide, N-methylpyrrolidinone, N,N-dimethylacetamide,tetramethylurea, and mixtures thereof; more preferably the first solventis selected from 1-hexanol, 1-heptanol, 2-ethyl-1-hexanol, 1-octanol,N,N-dimethylformamide, N-methylpyrrolidinone, N,N-dimethylacetamide,tetramethylurea, and mixtures thereof; still more preferably the firstsolvent is selected from 1-hexanol and N-methylpyrrolidinone.

As used herein, the term “aliphatic” refers to a hydrocarbon molecule orhydrocarbon moiety of a molecule that is not aromatic in structure.“Alkyl” refers to a hydrocarbon moiety of a molecule that is completelysingle-bonded, while the term “polyalkyl” refers to a molecular moietycontaining more than one alkyl group. “Polyalkylene” refers to amolecular moiety containing more than one divalent or multivalent alkylradical. The foregoing moieties may be cyclic, linear, or branched instructure.

1-Hexanol, N-methylpyrrolidinone and similar aliphatic alcohols andamides are preferred compounds for the first solvent in large partbecause they generally have adequate evaporation rates and flash points,and because they tend to dissolve polyamides resins to providelow-to-moderate viscosity solutions. Many are commercially available atlow to moderate cost and have bland (i.e., non-obnoxious) or evenpleasant odors. Furthermore, because they are good solvents forpolyamides, other solvents can be admixed in the ink without causing theink to gel or cloud even at the high resin loadings desired. Preferably,the first solvent is at least 20 wt % of the total solvent of the inkcomposition; more preferably the first solvent is 30-90 wt % of thetotal solvent of the ink composition; still more preferably the firstsolvent is 40-80 wt % of the total solvent of the ink composition; evenstill more preferably the first solvent is 45-75 wt % of the totalsolvent of the ink composition.

The second solvent, comprising up to 80% by weight of the solvent(considered separately from the polyamide and the colorant), is a liquidthat can be used to adjust the ink flash point, viscosity, polyamidesolubility and/or drying rate, but must be carefully selected in termsof chemical properties and quanitity so as not to cause the polyamideresin to precipitate from the ink or gel the ink. Selection of thesecond solvent is therefore very important and is preferably limited toliquids having a flash point greater than about 40° C. and a viscosityat 25° C. of less than 60 cps; more preferably the second solvent has aviscosity at 25° C. of less than 45 cps; even more preferably the secondsolvent has a viscosity at 25° C. of less than 30 cps; still even morepreferably the second solvent has a viscosity at 25° C. of less than 25cps.

In one aspect, the second solvent is a hydrocarbon. Preferred secondsolvents are cycloalkanes, fused cycloalkanes, alkenes, and dearomatizedmineral spirits. Hydrocarbons that can serve as the second solvent areexemplified by (without limitation) DECALIN™ decahydronaphthalene(DuPont), dearomatized mineral spirits, and terpene hydrocarbons.Terpene hydrocarbons are exemplified by (without limitation) α-pinene,β-pinene, limonene, and terpinolene.

In a preferred aspect of the invention, the first solvent is selectedfrom cyclohexanol, 1-hexanol, 2-hexanol, 3-hexanol, cis-2-hexen-1-ol,trans-2-hexen-1-ol, cycloheptanol, 1-heptanol, 2-heptanol,2-ethyl-1-hexanol, 1-octanol, 1-nonanol, 3,5,5-trimethyl-1-hexanol,1-decanol, α-terpineol, 3,7-dimethyl-3-octanol (tetrahydrolinalool), andmixtures thereof; and the second solvent is mineral spirits or afraction thereof. In a further preferred aspect of the invention, thefirst solvent is 1-hexanol or 1-heptanol and the second solvent ismineral spirits. In a separate preferred aspect of the invention, thefirst solvent is selected from N,N-dimethylformamide,N-methylpyrrolidinone, N,N-dimethylacetamide, tetramethylurea, andmixtures thereof, and the second solvent is a terpene hydrocarbon ormixture of terpene hydrocarbons. Preferably, the second solvent is up to80 wt % of the total solvent of the ink composition; more preferably thesecond solvent is 5-70 wt % of the total solvent of the ink composition;still more preferably the second solvent is 10-60 wt % of the totalsolvent of the ink composition; even still more preferably the secondsolvent is 15-55 wt % of the total solvent of the ink composition; yeteven still more preferably the second solvent is 25-50 wt % of the totalsolvent of the ink composition.

In an optional aspect of the invention, the solvent further comprises athird solvent selected from α-hydroxy-carboxylic ester, polyalkyleneglycol alkyl ether, and ketone-containing solvnets. Illustrative ofthese are (without limitation) methyl lactate, ethyl lactate, n-propyllactate, and isopropyl lactate as exemplary α-hydroxy-carboxylic esters;diethylene glycol methyl ether and dipropylene glycol methyl ether asexemplary polyalkylene glycol alkyl ethers; and cyclohexanone as anexemplary ketone-containing solvent. Preferably the third solvent isselected from ethyl lactate, dipropylene glycol methyl ether,cyclohexanone, and mixtures thereof. Also preferably, the third solventis up to 50% by weight of the organic solvent in the ink of theinvention; more preferably the third solvent is up to 40% by weight ofthe organic solvent in the ink of the invention; even more preferablythe third solvent is up to 35% by weight of the organic solvent in theink of the invention.

In other preferred aspects, the printing ink of the present inventionhas a viscosity of less than 25 cps at one or more temperatures between25° C. and 60° C., and/or said ink has a flash point of greater than 40°C. Ink viscosity, flash point, and solvent evaporation are threephysical properties of concern in inkjet inks, and more particularly inDOD inks. Because inks in DOD printers are typically allowed to standfor extended periods of time in the discharge orifices of the print headduring stand-by periods, if the ink is too viscous it likely willsolidify in the print head and clog the orifices. Similarly, if thesolvent of said ink is too volatile, there is increased likelihood thatthe ink solvent will evaporate over time, allowing the ink binder toconcentrate and become more viscous. In addition, the more volatile anink solvent, the greater the chance of flammable vapor accumulation,making such inks particularly unsafe for air transport, where conditionsof low atmospheric pressure and confined spaces prevail. Therefore, inkscomprising solvents with suitably high boiling points and flash pointsare preferred. Preferably, the printing ink of the present invention hasa flash point of greater than 40° C.; more preferably, the printing inkof the present invention has a flash point of greater than 50° C.; evenmore preferably the printing ink of the present invention has a flashpoint of greater than 55° C.; yet even more preferably the printing inkof the present invention has a flash point of greater than 60° C.

The ink vehicle (i.e., the ink less the colorant) consists of from about5% to 40% polyamide resin and from 35% to 95% by weight of the solvent.The colorant of the invention can be any one of numerous suitable dyesor pigments currently offered for sale for use in DOD inkjet inks.Suitable colorants are available from, for example, Clariant (Muttenz(near Basel), Switzerland), Ciba Speciality Chemicals (Basel,Switzerland), and Day-Glo Color (Cleveland, Ohio, USA). The colorant istypically present in the ink at a level of about 1-10% by weight, wherethis level may be increased or decreased depending on the desired colorinstensity of the ink, so long as viscosity values are not exceeded.

Ink preparation is well known and any one of the many art methods issatisfactory. For example, vehicle is first prepared by heating themixture of solvent and optional co-solvent to about 50-100° C. andadding, with stirring under an inert atmosphere, polyamide resinpellets. Stirring is continued until the resin dissolves. The mixture isthen cooled to about 30-60° C. and the dye or pigment charged withcontinued stirring until a homogeneous mixture is obtained. Forpigmented inks, this ink may be then fed through a shot mill or otherfinishing device to insure the pigment particles are broken down.Finally, the ink is filtered to remove particles too large to flowthrough the small nozzles of the DOD printer, and bottled.

The invention is illustrated in more detail by the following examples.In the following examples, chemicals were of reagent grade unless notedotherwise, and were obtained from commercial supply houses such asAldrich Chemical Co. (Milwaukee, Wis.). UNI-REZ® 2000-series dimer acidpolyamides, UNITOL™ BKS tall oil fatty acid, and UNIDYME™ 14 dimer acidwere obtained from Arizona Chemical (Jacksonville, Fla.). DOWANOL™ DPMdipropylene glycol methyl ether was obtained from The Dow Chemical Co.(Midland, Mich.). DBE is “dibasic esters”, a mixture of the refineddimethyl esters of adipic, glutaric and succinic acids which are allnaturally occurring materials. DBE, as well as ELVAX® 40Wpoly(vinylacetate) resin, DECALIN™ hydrocarbon solvent, and MYLAR™polymeric film, were obtained from DuPont (Wilmington, Del.). “Solvent142”, as referred to herein as “HC142” is mineral spirits as obtainedfrom Ashland, Inc. (Columbus, Ohio). UNITENE™ D and TERPINOLENE™ 90terpenes were obtained from International Flavors and Fragrances (NewYork, N.Y.). SCOTCH™ 600 and SCOTCH™ 610 cellophane tape were obtainedfrom 3M (St. Paul, Minn.). UCAR™ 500XP vinyl polymer resin was obtainedfrom Union Carbide (Danbury, Conn.).

EXAMPLE 1 Solvent Selection Criteria for Dimer Acid-Based PolyamideDigital Ink

TABLE 1 sets forth criteria that are evaluated when selecting a solventfor an ink composition according to the present invention. TABLE 1 WIDEFORMAT INK SOLVENT CRITERIA Criteria Type Criteria Level Desired Reasonfor Criteria Flash Point As close to 61° C. Allows shipment as non- aspossible hazardous Evaporation As high as possible Leads to faster printspeeds Rate Viscosity As low as possible Allows for more resin insolution Stability A 20% solids solution Must not change in viscosity ofresin must remain (or gel) when shipped by air. fluid even if chilledCost Good if same as glycol Some increased cost over current etherssolvent may be acceptable, but not desired. Toxicity A “2” health Highlytoxic solvents will rating or less; one require special (expensive) withan environmen- ventilation of the press. tally-friendly image would bebest. Odor A “pleasant” odor is Unpleasant solvents will best, “bland”is good. require special (expensive) ventilation of the press.

EXAMPLES 2-6 Candidate Protic Solvents for Formulating Low VolatilityDimer Acid-Based Polyamide Inkjet Inks

In these examples, various protic solvents were assessed as candidatesto solubilize polyamide resin selected from Arizona Chemical's UNI-REZ®2000-series of polymerized fatty acid-based polyamide resins. Thesesolvents were assessed according to criteria set forth in EXAMPLE 1.Solvent properties are summarized in TABLE 2.

Of the protic aliphatic solvents tested, 1-hexanol, having suitableresin solubility, the fastest evaporation rate and lowest viscosity ofthe tested alcohols having an acceptable flash point, exhibited the mostsuitable properties for use with dimer acid-based polyamide resins.However, all alcohols tested had high viscosities relative to othercandidate solvents (summarized in TABLE 2 and TABLE 3). Therefore, it isrecommended to use only enough of a protic aliphatic solvent as neededto stabilize the resin solution if so required.

Of the two protic polar solvents tested, neither ethyl lactate norDOWANOL™ DPM dipropylene glycol methyl ether dissolved polyamide resinas well as the protic aliphatic solvents. However, both of these proticpolar solvents may be used in small quantities with polyamide resin toadjust flash point, evaporation rate, and possibly adhesion tosubstrate. TABLE 2 PHYSICAL PROPERTIES OF CANDIDATE PROTIC SOLVENTS FORFORMULATING LOW VOLATILITY JET INKS Solvent Type PROTIC ALIPHATIC PROTICPOLAR Example 2 3 4 5 6 Name 1-Hexanol 2-Ethylhexanol 1-Octanol Ethyllactate DOWANOL ™ DPM CAS Number 111-27-3 104-76-7 111-87-5 687-47-834590-94-8 Flash Point (° C.) 60 73 81 49 78 Boiling Point (° C.) 156.5182 196 154 188 Freezing Point (° C.) −52 −76 −15 −26 −80 Viscosity (cps@ 25° C.) ca. 6 ca. 9 10.6(15° C.) 2.4 0.95 Evaporation Rate (% of BA)*0.05 0.01 — 0.21 0.03 Density (at 25° C.) 0.814 0.834(20° C.) 0.8271.042 0.951(20° C.) Odor Pleasant Light, fruity Unpleasant Fruity Bland,paint-like Preferred co-solvent? ++ + + − − (+: moderately; ++:strongly; −: not preferred)*100% evaporation rate is equated to the evaporation rate of n-butylacetate.

EXAMPLES 7-11 Candidate Aprotic Solvents for Formulating Low VolatilityDimer Acid-Based Polyamide Inkjet Inks

In these examples, various aprotic solvents were assessed as candidatesto solubilize polyamide resin selected from Arizona Chemical's UNI-REZ®2000-series of polymerized fatty acid-based polyamide resins. Thesesolvents were assessed according to criteria set forth in EXAMPLE 1.Solvent properties are summarized in TABLE 3.

Of the two aprotic polar solvents tested (cyclohexanone and, DBE),cyclohexanone exhibited better polyamide solubility, but would be toovolatile for use in more than minor portions. However, these solventsmay be used in minor amounts in order to provide improved flash points,evaporation rates, and/or solution stability.

Of the aprotic nonpolar solvents tested, all were shown to be suitablefor use with polymerized fatty acid-based polyamide resins, though mostsuitable when in admixture with at least one other solvent. Mineralspirits, as exemplified by Solvent 142, was inexpensive, had a blandodor, a low viscosity, a relatively high evaporation rate, and anoptimal flash point according to EXAMPLE 1. Accordingly, mineral spiritsis a preferred solvent for inclusion in the ink compositions of thepresent invention. Dipentene solvents such as UNITENE™ D terpene solventand in particular TERPINOLENE™ 90 terpene solvent, having mild pineodors and flash points greater than 49° C., were also good solvents foruse with dimer acid-based polyamide resins (data not shown). TABLE 3PHYSICAL PROPERTIES OF CANDIDATE APROTIC SOLVENTS FOR FORMULATING LOWVOLATILITY JET INKS Solvent Type APROTIC POLAR APROTIC NONPOLAR Example7 8 9 10 11 Name Cyclohexanone DBE Limonene Solvent 142 DECALIN ™ CASNumber 108-94-1 627-93-0 5989-27-5 64742-88-7 91-17-8 Flash Point (° C.)47 100 46 63 57 Boiling Point (° C.) 155 196-225 177 189-202 190Freezing Point (° C.) −47 −20 — — −125 Viscosity (cps @ 25° C.) 2.0 2.4(ca. 1.5) (ca. 1.5) (ca. 3) Evaporation Rate (% of BA) 0.29 0.01 — — —Density (at 25° C.) 0.947 1.097 — 0.782(16° C.) 0.896 Odor Fruity,cheesy Bland Citrus Bland, like Light, like mineral oil mineral oilPreferred co-solvent? − − + ++ + (+: moderately; ++: strongly; −: notpreferred)

EXAMPLES 12-16 Candidate Aprotic Tertiary Amide and Carbamide Solventsfor Formulating Low Volatility Dimer Acid-Based Polyamide Inkjet Inks

In these examples, various aprotic tertiary amide and carbamide solventswere assessed as candidates to solubilize polyamide resin selected fromArizona Chemical's UNI-REZ® 2000-series of polymerized fatty acid-basedpolyamide resins. These solvents were assessed according to criteria setforth in EXAMPLE 1. Solvent properties are summarized in TABLE 4.

Of the aprotic tertiary amide and carbamide solvents tested, NMP and TMUexhibited the most suitable properties for use with dimer acid-basedpolyamide resins, though each preferably in admixture with at least oneother solvent for optimal solvent usage. By contrast, DMF, having apungent fishy odor, and DMAC, being somewhat toxic, were deemed lesssuitable for use as solvents or co-solvents with dimer acid-basedpolyamide resins. In one aspect, NMP or TMU could be used to stabilizethese resins in solution, possibly in place of 1-hexanol or blended with1-hexanol to lower the solution viscosity. TABLE 4 PHYSICAL PROPERTIESOF CANDIDATE APROTIC TERTIARY AMIDE AND CARBAMIDE SOLVENTS FORFORMULATING LOW VOLATILITY JET INKS Solvent Type APROTIC TERTIARY AMIDESExample 12 13 14 15 16 Name Dimethyl- Tetramethyl- Dimethyl- N-Methyl-Dimethyl- formamide urea acetamide pyrrolidinone imidazolidinoneAbbreviated name DMF TMU DMAC NMP DMI CAS Number 68-12-2 632-22-4127-19-5 872-50-4 80-73-9 Flash Point (° C.) 57 66 70 91 80 BoilingPoint (° C.) 153 177 165 204 107 @ 17 mm Hg Freezing Point (° C.) −61 −1−20 −24 — Viscosity (cps @ 25° C.) 0.82 — 1.02 1.7 — Evaporation Rate (%of BA) 0.20 — — 0.06 — Density (at 25° C.) 0.938 0.971 0.937 1.04 1.044Odor Fishy Light amine; fishy Bland, pleasant Bland Light amine; fishyPreferred co-solvent? − ++ − ++ n.d.* (+: moderately; ++: strongly; −:not preferred)*n.d., not determined.

EXAMPLES 17-39 Viscosities of Candidate Resin Solvent Systems forFormulating Low Volatility Dimer Acid-Based Polyamide Inkjet Inks

These examples disclose viscosity values for various solvent systemsupon admixture with 20-30 wt % UNI-REZ® 2221 polymerized fattyacid-based polyamide resin. Results are summarized in TABLE 5.Comparative examples are denoted by “c” following the example number.TABLE 5 BROOKFIELD VISCOSITIES (CPS, 25° C.) OF TEST SOLUTIONS OFUNI-REZ ® 2221 20% 25% 30% Example Description of the Solvent or SolventBlend [wt:wt] Solids Solids Solids 17c 1-Hexanol 23.0 — 51.8 18cN-Methylpyrrolidinone (NMP) — — 24.0 19c Dimethylacetamide (DMAC) Ca. 5— 12.3 20c Dimethylimidazolidinone (DMI) — — 34.9 Two-component solventblends 21 Hexanol + DECALIN ™ [50:50] 20.9 — — 22 Hexanol + DECALIN ™[35:65] 22.0 — — 23 Hexanol + HC142 [67:33] 16.9 — — 24 Hexanol + HC142[40:60] — 23.0 — 25 Hexanol + HC142 [35:65] 13.4 22.4 40.0 26 2-EthylHexanol + TERPINOLENE ™ 90 [30:70] — 32.0 — 27 NMP + DECALIN ™ [43:57] —— 33.4 28 NMP + Limonene [80:20] — 14.3 — 29 NMP + Limonene [50:50] — —21.8 30 TMU + Limonene [50:50] — — 18.8 31 DMI + Limonene [50:50] — —23.5 32c NMP + DPM* [60:40] — — 35.7 33c NMP + Butyl Acetate [67:33] — —19.1 Multi-component solvent blends 34 Hexanol + DPM* + DECALIN ™[50:25:25] 19.8 — — 35 Hexanol + NMP + HC142 [33:33:33] — 17.4 — 36Hexanol + NMP + HC142 + Limonene [20:30:40:10] — 15.6 — 37 Hexanol +DPM* + DECALIN ™ [34:33:33] 19.7 — — 38 Hexanol + DMAC + DECALIN ™[12.5:37.5:50] 9.4 — 23.4 39 NMP + DPM* + HC142 + Limonene 12.3 — 32.5[33.3:33.3:25:8.3]*DPM: DOWANOL ™ DPM dipropylene glycol methyl ether.

EXAMPLES 40-44 Viscosities of Candidate Resin Solvent Systems forFormulating Low Volatility Dimer Acid-Based Polyamide Inkjet Inks

These examples disclose viscosity values for various solvent systemsupon admixture with 25-30 wt % UNI-REZ® 2224 polymerized fattyacid-based polyamide resin. Results are summarized in TABLE 6. TABLE 6VISCOSITY DATA FOR TEST SOLUTIONS OF UNI-REZ ® 2224 Description of theSolvent 25% 30% Example or Solvent Blend [wt:wt] Solids Solids 40Hexanol + Solvent 142 [40:60] 15.2 — 41 NMP + Limonene [80:20] 7.6 — 42NMP + Limonene [50:50] — 12.7 43 Hexanol + NMP + Solvent 142 11.6 —[33:33:33] 44 Hexanol + NMP + Solvent 142 + 10.2 — Limonene[20:30:40:10]

EXAMPLES 45-50 Viscosities of Candidate Resin Solvent Systems forFormulating Low Volatility Dimer Acid-Based Polyamide Inkjet Inks

These examples disclose viscosity values for various solvent systemsupon admixture with 15-20 wt % UNI-REZ® 2226 polymerized fattyacid-based polyamide resin. Results are summarized in TABLE 7. TABLE 7VISCOSITY DATA FOR TEST SOLUTIONS OF UNI-REZ ® 2226 Percentage of EachSolvent Component in Blend Brookfield Viscosity Data Mineral wt %Viscosity wt % Viscosity Example Spirits NMP Limonene Hexanol Resin(cps) Resin (cps) 45 40 — — 60 15 13.5 20 20.7 46 40 30 — 30 15 8.3 2014.1 47 40 30 15 15 15 Gelled 20 11.7 48 20 45 20 15 15 7.2 20 12.0 49 —60 25 15 15 7.4 20 12.7 50 — 75 25 — 15 7.2 20 11.7

EXAMPLES 51-56 Viscosities of Candidate Resin Solvent Systems forFormulating Low Volatility Dimer Acid-Based Polyamide Inkjet Inks

These examples disclose viscosity values for various solvent systemsupon admixture with 15-20 wt % UNI-REZ® 2215 polymerized fattyacid-based polyamide resin. Results are summarized in TABLE 8. TABLE 8VISCOSITY DATA FOR TEST SOLUTIONS OF UNI-REZ ® 2215 Percentage of EachSolvent Component in Blend Brookfield Viscosity Data Mineral wt %Viscosity wt % Viscosity Example Spirits NMP Limonene Hexanol Resin(cps) Resin (cps) 51 40 — — 60 15 16.7 20 29.5 52 40 30 — 30 15 10.8 2019 53 40 30 15 15 15 9.1 20 15.8 54 20 45 20 15 15 9.8 20 16.6 55 — 6025 15 15 10.1 20 17.1 56 — 75 25 — 15 9.3 20 16.2

EXAMPLES 57-77 Stability of Dimer Acid-Based Polyamide Resin Solutions

In these examples, solutions of UNI-REZ® 2221 polymerized fattyacid-based polyamide resin in various solvents were analyzed forsolution stability in terms of clarity, fluidity, and homogeneity.

Solutions of resin in indicated solvent systems were heated withstirring to about 100° C. for less than about 30 minutes under inertatmosphere. Solutions were then cooled to ambient temperature withstirring, then poured into covered glass containers and allowed to sitat ambient temperature for 24 hours. Samples were then subjected tothree sequential freeze-thaw cycles as follows: For the firstfreeze-thaw cycle samples were cooled to 0° C. for 24 hours, then warmedto 25° C. for 24 hours. For the second freeze-thaw cycle samples werecooled to 0° C. for 24 hours, then warmed to 25° C. for 24 hours. Forthe third freeze-thaw cycle samples were cooled to 0° C. for 48 hours,then warmed to 25° C. for 24 hours.

After each freeze-thaw cycle, vessels containing samples were gentlytipped and assessed for clarity, fluidity, and solution homogeneity.Samples determined to be clear, completely fluid and homogeneousthroughout a freeze-thaw cycle were deemed to have “passed” a solutionstability test and were then subjected to the next freeze-thaw cycle.Samples that became gelled upon freezing but that reverted to a clear,homogeneous and completely fluid state upon thawing were identified ashaving “recovered” from a solution stability test, and were thensubjected to the next freeze-thaw cycle. Samples that neither passed norrecovered from a solution stability test were deemed to have “failed”said solution stability test, and were not subjected to further testing.Results of the foregoing test procedure are summarized in TABLE 9. TABLE9 FREEZE-THAW STABILITY TESTING OF UNI-REZ ® 2221 SOLUTIONS Resin 1^(st)Amt. 2^(nd) 3^(rd) Amt. Frz/Thw Frz/Thw Frz/Thw Example Wt % Solvent %Solvent Amt. % Solvent % Cycle1 Cycle 2 Cycle3 57 20 Hexanol 67 Solvent33 — — Passed Passed Passed 142 58 20 Hexanol 50 Solvent 25 Cyclo- 25Passed Passed Passed 142 hexanone 59 20 Hexanol 50 Solvent 25 DPM# 25Passed Passed Passed 142 60 20 Hexanol 50 Solvent 25 Ethyl 25 PassedPassed Passed 142 lactate 61 20 Hexanol 50 Solvent 50 — — Passed PassedPassed 142 62 20 Hexanol 50 DECALIN ™ 50 — — Passed Passed Passed 63 20Hexanol 50 DECALIN ™ 25 DPM# 25 Passed Passed Passed 64 20 Hexanol 35Solvent 65 — — Passed Recovered Passed 142 65 20 Hexanol 35 DECALIN ™ 65— — Passed Passed Passed 66 20 Hexanol 35 Solvent 32.5 Cyclo- 32.5Passed Passed Passed 142 hexanone 67 20 Hexanol 35 DECALIN ™ 32.5 Cyclo-32.5 Passed Passed Passed hexanone 68 20 Hexanol 35 DECALIN ™ 32.5 DPM#32.5 Passed Passed Passed 69 20 2-Ethyl- 35 DECALIN ™ 32.5 Cyclo- 32.5Passed Passed Passed hexanol hexanone 70 20 2-Ethyl- 35 DECALIN ™ 65 — —Passed Recovered Failed* hexanol 71 30 Solvent 65 Hexanol 35 — — Failed— — 142 72 25 Solvent 65 Hexanol 35 — — Failed* — — 142 73 20 NMP 50Limonene 50 — — Passed Passed Passed 74 30 NMP 33 Solv. 142/ 25/8.3 DPM#33 Failed — — Limonene 75 20 NMP 33 Solv. 142/ 25/8.3 DPM# 33 Failed —Recovered Limonene 76 30 Limonene 50 NMP 50 — — Recovered RecoveredRecovered 77 30 NMP 42.9 DECALIN ™ 57.1 — — Passed Passed Recovered*Very slightly viscous.#DPM: DOWANOL ™ DPM dipropylene glycol methyl ether.

EXAMPLES 78-99 Comparative Stability of Dimer Acid-Based Polyamide ResinSolutions

In these examples, solutions of UNI-REZ® 2221 polymerized fattyacid-based polyamide resin in various solvents were analyzed forsolution stability in terms of clarity, fluidity, and homogeneity.Samples were prepared, treated, and analyzed in the manner described inEXAMPLES 57-77. Results are summarized in TABLE 10. TABLE 10 FREEZE-THAWSTABILITY TESTING OF UNI-REZ ® 2221 SOLUTIONS Resin 1^(st) Amt. 2^(nd)Amt. 3^(rd) Amt. Frz/Thw Frz/Thw Frz/Thw Example Wt % Solvent % Solvent% Solvent % Cycle1 Cycle 2 Cycle3 78 30 Hexanol 100 — — — — PassedPassed Recovered 79 25 Hexanol 100 — — — — Passed Passed Passed 80 20Hexanol 100 — — — — Passed Passed Passed 81 15 Hexanol 100 — — — —Passed Passed Passed 82 10 Hexanol 100 — — — — Passed Passed Passed 8320 Hexanol 67 — — Ethyl 33 Passed Passed Passed lactate 84 20 Hexanol 67— — DPM# 33 Passed Passed Passed 85 20 Hexanol 67 — — Cyclohexanone 33Passed Passed Passed 86 20 Hexanol 50 — — Cyclohexanone/ 25/25 PassedPassed Recovered DPM# 87 20 Hexanol 50 — — Ethyl lactate/ 25/25 PassedPassed Passed DPM# 88 20 Hexanol 50 — — DPM# 50 Failed — — 89 20 — — — —Cyclohexanone/ 50/50 Passed Passed Passed Ethyl lactate 90 20 Hexanol 35— — Cyclohexanone 65 Recovered Recovered Recovered 91 20 Hexanol 35 — —Cyclohexanone/ 32.5/ Recovered Recovered Recovered DPM# 32.5 92 202-Ethyl- 35 — — Cyclo- 65 Recovered Failed Failed* hexanol hexanone 9320 DMAC 100 — — — — Failed** — — 94 20 NMP 100 — — — — RecoveredRecovered Recovered 95 20 NMP 68.6 Butyl 31.4 — — Recovered RecoveredRecovered acetate 96 30 DMAC 100 — — — — Failed — — 97 30 NMP 100 — — —— Recovered Failed* — 98 30 NMP 69 Butyl 31 — — Failed — — acetate 99 20— — DECALIN ™ 50 Ethyl 50 Passed Passed Passed lactate*Very slightly viscous.**If shaken, almost recovers.#DPM: DOWANOL ™ DPM dipropylene glycol methyl ether.

EXAMPLES 100-102 Stability of Dimer Acid-Based Polyamide Resin Solutions

In these examples, solutions of UNI-REZ® 2224 polymerized fattyacid-based polyamide resin in various solvents were prepared andanalyzed for solution stability in terms of clarity, fluidity, andhomogeneity, in a manner similar to that described for the thirdfreeze-thaw cycle in EXAMPLES 57-77. Results of this analysis aresummarized in TABLE 11. TABLE 11 UNI-REZ ® 2224 FREEZE-THAW STABILITYTEST RESULTS Description of the Solvent or At 25% Example Solvent Blend[wt:wt] Solids 100 Hexanol + Solvent 142 [40:60] Recovered¹ 101 NMP +Limonene [80:20] Failed² 102 Solvent 142 + NMP + Hexanol + Failed²Limonene [40:30:20:10]¹Recovered after gelling during each of the three freeze periods.²Gelled during the first freeze period and did not recover fluidity whenwanned.

EXAMPLES 103-108 Stability of Dimer Acid-Based Polyamide Resin Solutions

In these examples, solutions of UNI-REZ® 2226 polymerized fattyacid-based polyamide resin in various solvents were prepared andanalyzed for solution stability in terms of clarity, fluidity, andhomogeneity, in a manner similar to that described for the thirdfreeze-thaw cycle in EXAMPLES 57-77. Results of this analysis aresummarized in TABLE 12. TABLE 12 FREEZE-THAW STABILITY RESULTS FOR TESTSOLUTIONS OF UNI-REZ ® 2226 Percentage of Each Solvent Component inBlend Freeze-Thaw Test Mineral wt % wt % Example Spirits NMP Limonene1-Hexanol Resin Result Resin Result 103 40 — — 60 15 Passed 20 Recovered104 40 30 — 30 15 Failed 20 Failed 105 40 30 15 15 15 Not Done 20 Failed106 20 45 20 15 15 Recovered 20 Failed 107 — 60 25 15 15 Passed 20Recovered 108 — 75 25 — 15 Passed 20 Recovered

EXAMPLES 109-114 Stability of Dimer Acid-Based Polyamide Resin Solutions

In these examples, solutions of UNI-REZ® 2215 polymerized fattyacid-based polyamide resin in various solvents were prepared andanalyzed for solution stability in terms of clarity, fluidity, andhomogeneity, in a manner similar to that described for the thirdfreeze-thaw cycle in EXAMPLES 57-77. Results of this analysis aresummarized in TABLE 13. TABLE 13 FREEZE-THAW STABILITY RESULTS FOR TESTSOLUTIONS OF UNI-REZ ® 2215 Percentage of Each Solvent Component inBlend Freeze-Thaw Test Mineral wt % wt % Example Spirits NMP Limonene1-Hexanol Resin Result Resin Result 109 40 — — 60 15 Passed 20 Passed110 40 30 — 30 15 Passed 20 Failed 111 40 30 15 15 15 Passed 20 Failed112 20 45 20 15 15 Passed 20 Passed 113 — 60 25 15 15 Passed 20 Passed114 — 75 25 — 15 Passed 20 Passed

EXAMPLES 115-123 Stability of Dimer Acid-Based Polyamide Resin inTerpene Solutions

In these examples, solutions of polymerized fatty acid-based polyamideresin in various solvents comprising terpene were prepared and analyzedfor viscosity and solution stability in terms of clarity, fluidity, andhomogeneity, in a manner similar to that described for the thirdfreeze-thaw cycle in EXAMPLES 57-77. Results of this analysis aresummarized in TABLE 14. TABLE 14 VISCOSITY AND FREEZE-THAW STABILITYRESULTS FOR TEST SOLUTIONS CONTAINING TERPENES Viscos- SolventTERPINOLENE ™ UNITENE ™ ity Cycle Example Resin wt % NMP Limonene 142 90D Hexanol (cps) Result 115 UNI-REZ ® 25 100 — — — — — 16.0 Failed 2221116 UNI-REZ ® 25 60 20 20 — — — 14.1 Recovered 2221 117 UNI-REZ ® 25 60— — 40 — — 14.6 Passed 2221 118 UNI-REZ ® 20 — — — — 67 33 24.4 Failed2215 119 UNI-REZ ® 25 100 — — — — — 27.4 Failed 2229 120# UNI-REZ ® 25100 — — — — — 26.9 Failed 2229 121 UNI-REZ ® 25 80 20 — — — — 24.9Recovered 2229 122 UNI-REZ ® 25 60 20 20 — — — 22.4 Recovered 2229 123UNI-REZ ® 20 — — 40 — — 60 23.7 Passed 2229#Replicate of Example 133.

EXAMPLES 124-133 Determination of Flash Points for Solutions of DimerAcid-Based Polyamide Resin

In these examples, flash points of solutions of UNI-REZ® 2221polymerized fatty acid-based polyamide resin in various solvent systemswere measured by the “closed cup method,” wherein a sample solution washeated in a closed vessel, a flame was applied to the vapor space abovesaid solution, and the temperature at which vapor ignition occurred wasdefined as the flash point for said solution. Measurement results aresummarized in TABLE 15. Comparative examples are denoted by “c”following the example number. TABLE 15 FLASH POINTS OF TEST SOLUTIONS OFUNI-REZ ® 2221 Percentage of Each Solvent Component in Blend wt % ClosedCup Mineral Amyl UNI-REZ ® Flash Example Spirits Acetate NMP Limonene1-Hexanol 2221 Point(° C.) 124 — — 100 — — 20 88 125 — — 84 16 — 20 64126 — — 80 20 — 25 63 127 — — 69 31 — 20 57 128 — — 69 31 — 30 58 129 50— — — 50 25 56 130 40 — — — 60 25 58 131 40 — 30 10 20 25 59 132c — 3169 — — 30 54 133c — 20 60 20 — 30 54

EXAMPLES 134-139 Determination of Flash Points for Blended TerpeneSolutions

In these examples, flash points blended monoterpene solvent systems weremeasured by the “closed cup method,” wherein a sample solution washeated in a closed vessel, a flame was applied to the vapor space abovesaid solution, and the temperature at which vapor ignition occurred wasdefined as the flash point for said solution. Measurement results aresummarized in TABLE 16. TABLE 16 FLASH POINTS OF TEST BLENDS OFMONO-TERPENES UNITENE ™ TERPINOLENE ™ Flash Point Example NMP D 90 (°C.) 134 70 0 30 64 135 50 0 50 64 136 30 0 70 62 137 80 20 0 64 138 7030 0 60 139 60 40 0 58

EXAMPLES 140-151 Adhesion Performance of Polymerized Fatty Acid-BasedPolyamide Resins

In these examples, solutions of polyamide resin are drawn on selectedsubstrates and tested for adhesion to said substrates by using tape toassess the extent of resin release.

Selected polymerized fatty acid-based polyamide resins (typically as a20 wt % solution in hexanol) were applied as a thin film onto selectedpolymeric substrates (vinyl, polyethylene (LLDPE), polypropylene (PP),or MYLAR™), and allowed to dry at least overnight. Then, strips ofSCOTCH™ 600 or SCOTCH™ 610 cellophane tape were applied as strips 4-8inches in length, across the resin-coated substrates, leaving no airpockets between tape and substrates. Tape strips were then removed bypulling at a 180° angle to the substrate, doing so with steadyconsistent movement. The test was then repeated in several locationsthroughout each coated substrate. The resin was deemed to have “passed”the adhesion test if no resin was transferred to the tape; otherwise theresin was deemed to have “failed” the adhesion test. Results of thesetests are summarized in TABLE 17. TABLE 17 ADHESIVE TAPE TEST RESULTSExample Resin Resin Type Vinyl LLDPE PP MYLAR ™ 140 UNI-REZ ® 2930Conventional Polyamide Passed Failed Passed Passed 141 UNI-REZ ® 2221Conventional Polyamide Passed Passed Passed Passed 142 UNI-REZ ® 2215Conventional Polyamide Passed Failed Passed Passed 143 UN1-REZ ® 2209Conventional Polyamide Passed Passed Passed Passed 144 0014-123-A¹ EDA +HMDA Polyamide Passed Passed Passed Passed 145 0014-104-A² PACMPolyamide Passed Failed Passed Passed 146 0018-61-B³ DACH PolyamidePassed Failed Failed Passed 147 0018-54-A⁴ BAPP Polyamide Failed FailedFailed Failed 148 0018-51-B⁵ IPDA Polyamide Passed Failed Failed Failed149 Surcol 836⁶ Polyacrylate Passed Passed Passed Passed 150 UCAR ™500XP Proprietary vinyl polymer Passed Failed Failed Failed 151 ELVAX ®40W Poly(vinylacetate) Passed Failed Failed Failed¹This resin is formed by reacting UNITOL ™ BKS tall oil fatty acid, 18.2wt %, UNIDYME ™ 14 dimer acid, 65.3 wt %, sebacic acid, 2.8 wt %,hexamethylene diamine, 4.7 wt %, and ethylene diamine, 9.1 wt %.²This resin is formed by reacting UNITOL ™ BKS tall oil fatty acid, 14.6wt %, UNIDYME ™ 14 dimer acid, 58.8 wt %, and bis(aminocyclohexyl)methane, 26.6 wt %. This resin has a 95° C. softening point.³This resin is formed by reacting UNITOL ™ BKS tall oil fatty acid, 18.4wt %, UNIDYME ™ 14 dimer acid, 60.1 wt %, adipic acid, 3.5 wt %, and1,2-diaminocyclohexane, 18.0 wt %.⁴This resin is formed by reacting propionic acid, 5.7 wt %, UNIDYME ™ 14dimer acid, 44.6 wt %, adipic acid, 11.3 wt %, and bis(aminopropyl)piperazine, 38.3 wt %. This resin has a 169.5° C. softening point.⁵This resin is formed by reacting UNITOL ™ BKS tall oil fatty acid, 26.3wt %, UNIDYME ™ 14 dimer acid, 10.6 wt %, adipic acid, 24.2 wt %, andisophorone diamine, 38.8 wt %. This resin has a 124° C. softening point.⁶This commercial acrylate resin had a viscosity at 10% in DOWANOL ™ DPMof 23.4 cps at 25° C.

From the foregoing it will be appreciated that, although specificembodiments of the invention have been described herein for purposes ofillustration, various modifications may be made without deviating fromthe spirit and scope of the invention. Accordingly, the invention is notlimited except as by the appended claims.

All of the above U.S. patents, U.S. patent application publications,U.S. patent applications, foreign patents, foreign patent applicationsand non-patent publications referred to in this specification and/orlisted in the Application Data Sheet, are incorporated herein byreference, in their entirety.

1. A method of printing, comprising charging a printhead of an inkjetprinter with ink, the ink being a fluid homogeneous mixture comprisingpolymerized fatty acid-based polyamide resin, organic solvent andcolorant, wherein the organic solvent comprises a first solvent and asecond solvent, where the first solvent comprises at least one solventselected from solvents comprising a single amide, a single carbamide, ora single hydroxyl group as the only non-hydrocarbon moiety in thesolvent; and the second solvent comprises at least one hydrocarbonsolvent; and transferring the ink from the printhead onto a substrate.2. The method of claim 1 wherein the printer is a drop-on-demandprinter.
 3. The method of claim 1 wherein the first solvent is at least20% by weight, and the second solvent is up to 80% by weight of theorganic solvent in the ink.
 4. The method of claim 1 wherein the firstsolvent comprises at least one of N-methylpyrrolidinone,N,N-dimethylformamide, N,N-dimethylacetamide, and tetramethylurea; andthe second solvent comprises at least one terpene hydrocarbon.
 5. Themethod of claim 1 wherein the first solvent comprises at least onealcohol solvent selected from the group consisting of cyclohexanol,1-hexanol, 2-hexanol, 3-hexanol, cis-2-hexen-1-ol, trans-2-hexen-1-ol,cycloheptanol, 1-heptanol, 2-heptanol, 2-ethyl-1-hexanol, 1-octanol,1-nonanol, 3,5,5-trimethyl-1-hexanol, 1-decanol, α-terpineol, and3,7-dimethyl-3-octanol (tetrahydrolinalool); and the second solventcomprises mineral spirits or a fraction thereof.
 6. The method of claim1 wherein the organic solvent further comprises a third solvent selectedfrom α-hydroxy-carboxylic ester, polyalkylene glycol alkyl ether, andketone-containing solvents.
 7. The method of claim 6 wherein the thirdsolvent is selected from methyl lactate, ethyl lactate, n-propyllactate, isopropyl lactate, diethylene glycol methyl ether, dipropyleneglycol methyl ether, and cyclohexanone.
 8. The method of claim 6 whereinthe third solvent is up to 50% by weight of the organic solvent in theink.
 9. A printing ink composition comprising colorant, resin andsolvent, where the resin is a polymerized fatty acid-based polyamideresin, the solvent comprises a first solvent and a second solventwherein the first solvent comprises at least one solvent having a singleamide group or a single carbamide group as the only non-hydrocarbonmoiety in the solvent; and the second solvent comprises at least onehydrocarbon solvent.
 10. The printing ink of claim 9 wherein the firstsolvent is at least 20% by weight, and the second solvent is up to 80%by weight of the organic solvent in the ink.
 11. The printing ink ofclaim 9 wherein the components of the first solvent each have a total of5 to 11 atoms selected from carbon, nitrogen, and oxygen.
 12. Theprinting ink of claim 11 wherein the first solvent comprises at leastone of N-methylpyrrolidinone, N,N-dimethylformamide,N,N-dimethylacetamide, and tetramethylurea.
 13. The printing ink ofclaim 9 wherein the second solvent has a viscosity of less than 60 cpsat 25° C.
 14. The printing ink of claim 9 wherein the second solventcomprises at least one terpene hydrocarbon.
 15. The printing ink ofclaim 14 wherein the second solvent comprises at least one terpeneselected from the group consisting of α-pinene, β-pinene, limonene, andterpinolene.
 16. The printing ink of claim 12 or 14 wherein the firstsolvent comprises at least one of N-methylpyrrolidinone,N,N-dimethylformamide, N,N-dimethylacetamide, and tetramethylurea; andthe second solvent comprises at least one terpene hydrocarbon.
 17. Theprinting ink of claim 12 or 14 wherein the first solvent comprisesN-methylpyrrolidinone and the second solvent comprises terpinolene. 18.The printing ink of claim 9 wherein the organic solvent furthercomprises a third solvent selected from α-hydroxy-carboxylic ester,polyalkylene glycol alkyl ether, and ketone.
 19. The printing ink ofclaim 18 wherein the third solvent is selected from methyl lactate,ethyl lactate, n-propyl lactate, isopropyl lactate, diethylene glycolmethyl ether, dipropylene glycol methyl ether, and cyclohexanone. 20.The printing ink of claim 18 wherein the third solvent is up to 50% byweight of the organic solvent in the ink.
 21. The printing ink of claim9 wherein the polyamide is the reaction product of reactants comprisingpolymerized fatty acid, ethylene diamine, hexamethylenediamine, andfatty acid.
 22. The printing ink of claim 9 wherein the resin comprises5-40 wt % of the total weight of resin and solvent.
 23. The printing inkof claim 9 wherein the solvent comprises at least 30 wt % of the totalweight of resin and solvent.
 24. The printing ink of claim 9 having aviscosity of less than 25 cps at one or more temperatures between 25° C.and 60° C.
 25. The printing ink of claim 9 having a flash point ofgreater than 40° C.
 26. A printing ink composition comprising colorant,resin and solvent, where the resin is a polymerized fatty acid-basedpolyamide resin, the solvent comprises a first solvent and a secondsolvent, where the first solvent comprises at least one solvent having asingle hydroxyl group as the only non-hydrocarbon moiety in the solvent;and the second solvent comprises at least one hydrocarbon.
 27. Theprinting ink of claim 26 wherein the first solvent is at least 20% byweight, and the second solvent is up to 80% by weight of the organicsolvent in the ink.
 28. The printing ink of claim 26 wherein thecomponents of the first solvent each have a total of 5 to 11 atomsselected from carbon and oxygen.
 29. The printing ink of claim 28wherein the first solvent comprises a hydroxyl-containing solventselected from the group consisting of cyclohexanol, 1-hexanol,2-hexanol, 3-hexanol, cis-2-hexen-1-ol, trans-2-hexen-1-ol,cycloheptanol, 1-heptanol, 2-heptanol, 2-ethyl-1-hexanol, 1-octanol,1-nonanol, 3,5,5-trimethyl-1-hexanol, 1-decanol, α-terpineol, and3,7-dimethyl-3-octanol (tetrahydrolinalool).
 30. The printing ink ofclaim 26 wherein the second solvent has a viscosity of less than 60 cpsat 25° C.
 31. The printing ink of claim 26 wherein the second solventcomprises mineral spirits or a fraction thereof.
 32. The printing ink ofclaim 29 or 31 wherein the first solvent comprises 1-hexanol or1-heptanol and the second solvent comprises mineral spirits.
 33. Theprinting ink of claim 26 wherein the organic solvent further comprises athird solvent selected from α-hydroxy-carboxylic ester, polyalkyleneglycol alkyl ether, and ketone.
 34. The printing ink of claim 33 whereinthe third solvent is selected from methyl lactate, ethyl lactate,n-propyl lactate, isopropyl lactate, diethylene glycol methyl ether,dipropylene glycol methyl ether, and cyclohexanone.
 35. The printing inkof claim 33 wherein the third solvent is up to 50% by weight of theorganic solvent in the ink.
 36. The printing ink of claim 26 wherein thepolyamide is the reaction product of reactants comprising polymerizedfatty acid polyamide, ethylene diamine, hexamethylenediamine, and fattyacid.
 37. The printing ink of claim 26 wherein the resin comprises 5-40wt % of the total weight of resin and solvent in the ink.
 38. Theprinting ink of claim 26 wherein the solvent comprises at least 30 wt %of the total weight of resin and solvent.
 39. The printing ink of claim26 having a viscosity of less than 25 cps at one or more temperaturesbetween 25° C. and 60° C.
 40. The printing ink of claim 26 having aflash point of greater than 40° C.